A retaining subassembly for fixing a flange portion which is provided on a brake device to a bulkhead of a motor vehicle which separates an engine compartment from a vehicle inner space is known, for example, from DE 44 03 466 A1 which is incorporated by reference. The retaining subassembly has two stay bolts which are introduced from the flange portion of the brake device through the bulkhead into the vehicle inner space and which have to be screwed from the vehicle inner space. The complexity for fitting and removing the brake device again is consequently considerable as a result of the poor accessibility of the bulkhead in the vehicle inner space. Furthermore, the brake device has to be supported in the engine compartment at the same time in order to prevent it from tilting and falling out.